111
and crystallinity, the degree of crosslinking and polymer chain (Pillai and SinhaRay 2015). For example, a higher degree of polymer crystallinity decreases the rate
of gas transmission, because the crystallites do not allow the gas molecules to permeate through the polymer, while the amorphous regions limit the permeation
through the semicrystalline polymers (Siracusa 2012). In addition, platelet-shape
fillers show better permeability performances than fillers more compact shaped
(Duncan 2011). In contrast, some nano-fillers cause an increase in the permeability
when the polymer does not wet the filler.
6.5.2 Mechanical Properties
The purpose of the packaging is to protect the food from undesirable external influences and deficiencies such as random breaks and cracks in the material (Zeman
2007). The mechanical properties of a biobased polymer, such as E, maximum stress
(σ max ), strain at break (ε b ) and tenacity (T), should be improved for food packaging
applications. The formation of biobased nanocomposites with fillers has the potential
to obtain excellent mechanical properties when low levels of filler (<5 wt.%) are
incorporated. The mechanical performance of the nanocomposites depends on the
concentration, shape, size and orientation of the fillers (Youssef 2013). Such improvement in mechanical properties can be attributed to the high aspect ratio of nano-fillers
and their stiffness, which in turn changes the mobility and the relaxation behavior of
molecules (Azizi Samir et al. 2005). A good adhesion at the filler- polymer interface
increases the E and σ max values and heat resistance, while improving the shear resistance, exfoliation and corrosion resistance (Hussain et al. 2006).
6.5.3 Optical Properties
The optical properties of food packaging films, such as light transmission, exhibition of color and surface brightness, are important for the stability of the shelf life
of packaged foods, as well as for consumer satisfaction (Robertson 2013). The
transparency and UV-light barrier properties of polymer nanocomposites are the
most important parameters along with their clarity, haze, color, brightness and
refractive index. Biobased nanocomposite systems providing UV-barrier properties
by adding metals and their oxides (i.e. Ag, Al 2 O 3 , MgO, TiO 2 , ZnO) or clays are
important (Hsieh et al. 2006; Vartiainen et al. 2010; Du et al. 2012; Kanmani and
Rhim 2014). The optical properties of a nanocomposite are dependent on the size,
dispersion/distribution, nano-filler concentration and the application techniques.
When well-distributed nano-fillers are used, polymer nanocomposites show similar
transparency compared to pure polymer matrices, because fillers that are smaller
than the visible light wavelength cannot block the light (Fischer 2003).
6 Functional Biobased Composite Polymers for Food Packaging Applications
and crystallinity, the degree of crosslinking and polymer chain (Pillai and SinhaRay 2015). For example, a higher degree of polymer crystallinity decreases the rate
of gas transmission, because the crystallites do not allow the gas molecules to permeate through the polymer, while the amorphous regions limit the permeation
through the semicrystalline polymers (Siracusa 2012). In addition, platelet-shape
fillers show better permeability performances than fillers more compact shaped
(Duncan 2011). In contrast, some nano-fillers cause an increase in the permeability
when the polymer does not wet the filler.
6.5.2 Mechanical Properties
The purpose of the packaging is to protect the food from undesirable external influences and deficiencies such as random breaks and cracks in the material (Zeman
2007). The mechanical properties of a biobased polymer, such as E, maximum stress
(σ max ), strain at break (ε b ) and tenacity (T), should be improved for food packaging
applications. The formation of biobased nanocomposites with fillers has the potential
to obtain excellent mechanical properties when low levels of filler (<5 wt.%) are
incorporated. The mechanical performance of the nanocomposites depends on the
concentration, shape, size and orientation of the fillers (Youssef 2013). Such improvement in mechanical properties can be attributed to the high aspect ratio of nano-fillers
and their stiffness, which in turn changes the mobility and the relaxation behavior of
molecules (Azizi Samir et al. 2005). A good adhesion at the filler- polymer interface
increases the E and σ max values and heat resistance, while improving the shear resistance, exfoliation and corrosion resistance (Hussain et al. 2006).
6.5.3 Optical Properties
The optical properties of food packaging films, such as light transmission, exhibition of color and surface brightness, are important for the stability of the shelf life
of packaged foods, as well as for consumer satisfaction (Robertson 2013). The
transparency and UV-light barrier properties of polymer nanocomposites are the
most important parameters along with their clarity, haze, color, brightness and
refractive index. Biobased nanocomposite systems providing UV-barrier properties
by adding metals and their oxides (i.e. Ag, Al 2 O 3 , MgO, TiO 2 , ZnO) or clays are
important (Hsieh et al. 2006; Vartiainen et al. 2010; Du et al. 2012; Kanmani and
Rhim 2014). The optical properties of a nanocomposite are dependent on the size,
dispersion/distribution, nano-filler concentration and the application techniques.
When well-distributed nano-fillers are used, polymer nanocomposites show similar
transparency compared to pure polymer matrices, because fillers that are smaller
than the visible light wavelength cannot block the light (Fischer 2003).
6 Functional Biobased Composite Polymers for Food Packaging Applications